1. Field of the Invention
The present invention relates to a power supply circuit incorporated in a semiconductor integrated circuit and a booster power supply circuit that boosts an input voltage.
2. Description of the Related Art
In a semiconductor integrated circuit operated by a battery voltage, a power supply circuit that stabilizes a power supply voltage is incorporated. Furthermore, a booster power supply circuit that boosts a battery voltage may be incorporated. FIG. 1 shows an example of a conventional booster power supply circuit incorporated in a semiconductor integrated circuit. The booster power supply circuit performs twofold boosting. When switches S2 and S4 are turned on, a capacitor C1 is electrically charged with an input voltage Vin. When switches S1 and S3 are turned on, a capacitor C2 is electrically charged with the input voltage Vin through the capacitor C1. The operations are repeated to generate an output voltage Vout corresponding to 2Vin.
In a conventional circuit, by a simple switch changeover operation, a boosted voltage can be easily obtained. However, when the input voltage Vin changes, the value of the output voltage Vout changes accordingly, and an output voltage having a constant value cannot be always obtained. In order to try to stabilize the obtained output voltage Vout, a circuit configuration becomes complex, and a current consumption increases to deteriorate an output current capability.
In FIG. 7 described in Jpn. Pat. Appln. KOKAI Publication No. 2006-178018, a booster power supply circuit using a plurality of capacitors and a plurality of switches is disclosed.